All aircraft, large and small, production or experimental, depend on gyroscopes for a variety of navigational data. Most aircraft utilize mechanical or spinning-mass gyros to derive information, such as heading and attitude. Often housed in a remote location, an aircraft's gyro (or gyros) feed data back to a cockpit, which are displayed in a variety of instruments.
The standard primary instruments in small aircraft, such as experimental airplanes, or aircraft used in general aviation, include an attitude indicator, a heading indicator, and a turn coordinator/slip-skid indicator. An attitude indicator, also known as an artificial horizon, shows the relationship of a nose and wings to an aircraft's horizontal plane. In addition, a heading indicator, also known as a directional gyro, is used to counteract errors that occur in a magnetic compass during turns, speed changes, and turbulence. A turn coordinator/slip-skid indicator measures the rate and quality of a turn. During IFR (Instrument Flight Rules) flight, these instruments, especially an attitude indicator, are pilot's means of determining an aircraft's situation.
The standard primary instruments in small aircraft currently contain vacuum or electrically-driven mechanical gyroscopes. Loss of vacuum or electrical power, especially during instrument flight, renders these instruments useless and can result in pilot disorientation and, at times, fatal crashes.
There is an increasing focus within the aviation industry about the failure of mechanical gyroscopes and the lack of proper backup systems. The FAA recently published a safety pamphlet entitled “The Silent Emergency” that emphatically states that pilots of small aircraft should install backup systems for their aircraft. In addition, the Experimental Aircraft Association (EAA) is also actively promoting the adoption of standby gyroscopic navigation system.
A standby gyroscopic navigation system has been used in many commercial aircraft. Typically, in a commercial aircraft, a second set of primary instruments are installed independently as a standby navigation system to ensure that there are at least one set of properly functioned gyroscopes, in case that vacuum or electrical power of the other system fails. However, the cost of having a second set of primary instruments is prohibitively expensive for a small aircraft. In addition, a small aircraft is extremely sensitive to extra weight. Further, cockpit size and instrument panel space are very limited in small aircraft.
Other types of standby navigation systems have been developed, for example, Goodrich ESIS GH-3000 system. The Goodrich system is an electronic standby instrument system. The system provides navigation information such as attitude, altitude, airspeed, heading, etc., and the information is presented on a screen display. However, the system is not user-friendly. According to the Goodrich system's Pilot Guide, the attitude, altitude, airspeed, heading, and other navigation features are not displayed on a LCD screen display simultaneously. The Goodrich system displays navigation features on different screens selected by a mode selector. A pilot must change the screens to obtain different navigation features in flight. This increases pilot's cockpit management load, thereby reducing overall pilot awareness, which is considered dangerous in operating a small aircraft. In addition, the Goodrich system is generally too heavy and too costly for a small aircraft.
One of the main parameters related to performance of an electronic instrument system is signal-to-noise ratio. Typically, there are two types of noise; random noise and correlated noise. Random noise are typically caused by characteristics of a device, such as the sensitivity of a sensor, etc. Factors that contribute to correlated noise include temperature, vibration, electromagnetic fields, etc. Discrimination between signal and noise determines the performance of an electronic instrument system.
Another parameter related to performance of an electronic instrument is the drift of indication, often referred to as dynamic stability. For example, when an aircraft makes a constant angle turn and holds at that angle, gyro instruments should indicate holding at that angle as well. However, due to the instability, gyro instruments can only hold for a certain period of time and then tend to drift back to a level position. Even though an aircraft does not normally turn and hold an angle for longer than 3 minutes, the drift is an important parameter for performance. Typically, existing standby instrument systems can hold about 3-4 minutes before drifting back to a level position. It is desirable to have a system with longer holding time.
Accordingly, there is a need for an improved electronic navigation system. More specifically, there is a need for a compact, lightweight, cost effective electronic navigation system with higher signal-to-noise ratio and better dynamic stability.